During development mammals demonstrate a transition from suckling to chewing behavior for the ingestion of nutrients. These behaviors and the transition between them are essential for normal development and survival. Two critical components comprising the neural circuitry responsible for oral-motor behaviors are trigeminal motoneurons and mesencephalic trigeminal neurons. Insight regarding oral-motor development will be gained by correlating the development of terminals innervating trigeminal motoneurons and mesencephalic trigeminal neurons with the development of neurotransmitter receptor complexes utilized to modulate the activity of these neurons. This study will be the first to characterize oral-motor development using chemical neuroanatomical techniques. This will be accomplished by correlating changes in the glutamatergic and GABAergic innervation of trigeminal motoneurons and mesencephalic trigeminal neurons with the ontogeny of NMDA, AMPA, and GABAa receptors in these neurons during early postnatal development. Three different experimental protocols will be performed on rats at postnatal day 1, 5, 15, and 25 as these ages represent critical periods in oral-motor development. In the first set of experiments, a polyclonal antibody against glutamate and a polyclonal antibody against glutamate decarboxylase (GAD) will be used to label glutamatergic and GABAergic terminals throughout the trigeminal motor nucleus and mesencephalic trigeminal nucleus. In the second set of experiments, receptor immunohistochemistry using antibodies against NMDA, AMPA, and GABAa subunits will be used to describe the temporal and spatial expression of NMDA, AMPA, and GABAa receptors in trigeminal motoneurons and mesencephalic trigeminal neurons. Finally, quantitative receptor autoradiography using [3H]MK-801, [3H]AMPA, and [3H]muscimol will be used to determine density changes of NMDA, AMPA and GABAa receptors respectively. The results from these studies will provide insight into the role of glutamate and GABA in controlling neonatal trigeminal motoneuron and mesencephalic trigeminal neuron activity in order to further understand the development and function of early oral-motor circuits.